CHARLOTTE, N.C. – Some parents of CMS students are concerned after a second fire on a CMS bus in the past month.

In both cases, the bus was a Thomas CAT 3126 model and investigators have not determined a cause for either fire.

In the fire last Tuesday and in the fire on October 19, the fires appeared to start for no obvious reason in the engine compartments.

RELATED: Manufacturer joins CMS investigation of bus fire

One parent, Cary McCaskill wondered, “Is it a fluke thing that’s happening or is it something reoccurring and potentially endangering children unnecessarily?"

No one was injured in Tuesday’s fire, as was the case with an earlier bus fire in the past month.

In both cases, the buses were Thomas CAT 3126 models.

CMS said Thursday in a statement that the cause of the most recent fire has not been determined.

CMS said after the first fire all other CAT 3126 model buses were inspected, “with no areas of concern found,” according to the statement. CMS Transportation Services provided an update on October 23 to all technicians to ensure a thorough mechanical inspection of all buses that utilize the Freightliner 3126 engine.

In that update, it was determined that wires connected to the starter motor may have shorted out on the bus’s frame or a bracket holding them, or that the starter motor itself suffered a catastrophic failure.

As part of the further inspection of all buses with 3126 engines, technicians are advised to inspect the rubber sleeves protecting the wires and to replace or repair them as necessary. These instructions were shared with officials at the North Carolina Department of Instruction Transportation Division.

RELATED: Parents demand answers after CMS school bus fire

Some parents believe CMS should pull the buses of that type and model off the road until a cause can be determined.

CMS Chief Operating Officer Carol Stamper said yesterday there is no concrete plan in place for what to do if a cause can’t be determined.

Stamper said, “We have not discussed it to that extent, but I think we are all thinking in the back of our minds what Plan B may have to be.”

CMS said in their statement Thursday that a representative from Thomas Built, the manufacturer of the bus is taking part in the investigation.